eb57277ba3
When trying to write a MIDX, we already prevent the case where there
weren't any packs present, and thus we would have written an empty MIDX.
But there is another "empty" case, which is more interesting, and we
don't yet handle. If we try to write a MIDX which has at least one pack,
but those packs together don't contain any objects, we will encounter a
BUG() when trying to use the bitmap corresponding to that MIDX, like so:
$ git rev-parse HEAD | git pack-objects --revs --use-bitmap-index --stdout >/dev/null
BUG: pack-revindex.c:394: pack_pos_to_midx: out-of-bounds object at 0
(note that in the above reproduction, both `--use-bitmap-index` and
`--stdout` are important, since without the former we won't even both to
load the .bitmap, and without the latter we wont attempt pack reuse).
The problem occurs when we try to discover the identity of the
preferred pack to determine which range if any of existing packs we can
reuse verbatim. This path is: `reuse_packfile_objects()` ->
`reuse_partial_packfile_from_bitmap()` -> `midx_preferred_pack()`.
#4 0x000055555575401f in pack_pos_to_midx (m=0x555555997160, pos=0) at pack-revindex.c:394
#5 0x00005555557502c8 in midx_preferred_pack (bitmap_git=0x55555599c280) at pack-bitmap.c:1431
#6 0x000055555575036c in reuse_partial_packfile_from_bitmap (bitmap_git=0x55555599c280, packfile_out=0x5555559666b0 <reuse_packfile>,
entries=0x5555559666b8 <reuse_packfile_objects>, reuse_out=0x5555559666c0 <reuse_packfile_bitmap>) at pack-bitmap.c:1452
#7 0x00005555556041f6 in get_object_list_from_bitmap (revs=0x7fffffffcbf0) at builtin/pack-objects.c:3658
#8 0x000055555560465c in get_object_list (ac=2, av=0x555555997050) at builtin/pack-objects.c:3765
#9 0x0000555555605e4e in cmd_pack_objects (argc=0, argv=0x7fffffffe920, prefix=0x0) at builtin/pack-objects.c:4154
Since neither the .bitmap or MIDX stores the identity of the
preferred pack, we infer it by trying to load the first object in
pseudo-pack order, and then asking the MIDX which pack was chosen to
represent that object.
But this fails our bounds check, since there are zero objects in the
MIDX to begin with, which results in the BUG().
We could catch this more carefully in `midx_preferred_pack()`, but
signaling the absence of a preferred pack out to all of its callers is
somewhat awkward.
Instead, let's avoid writing a MIDX .bitmap without any objects
altogether. We catch this case in `write_midx_internal()`, and emit a
warning if the caller indicated they wanted to write a bitmap before
clearing out the relevant flags. If we somehow got to
write_midx_bitmap(), then we will call BUG(), but this should now be an
unreachable path.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
|
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README.md
Git - fast, scalable, distributed revision control system
Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.
Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-<commandname>.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with man gittutorial or git help tutorial, and the
documentation of each command with man git-<commandname> or git help <commandname>.
CVS users may also want to read Documentation/gitcvs-migration.txt
(man gitcvs-migration or git help cvs-migration if git is
installed).
The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission). To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org. The mailing list archives are available at https://lore.kernel.org/git/, http://marc.info/?l=git and other archival sites.
Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.
The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (depending on your mood):
- random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
- "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks